Systems and methods for finding regions of interest in hematoxylin and eosin (h&amp;e) stained tissue images and quantifying intratumor cellular spatial heterogeneity in multiplexed/hyperplexed fluorescence tissue images

ABSTRACT

Graph-theoretic segmentation methods for segmenting histological structures in H&amp;E stained images of tissues. The method relies on characterizing local spatial statistics in the images. Also, a method for quantifying intratumor spatial heterogeneity that can work with single biomarker, multiplexed, or hyperplexed immunofluorescence (IF) data. The method is holistic in its approach, using both the expression and spatial information of an entire tumor tissue section and/or spot in a TMA to characterize spatial associations. The method generates a two-dimensional heterogeneity map to explicitly elucidate spatial associations of both major and minor sub-populations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) from U.S.provisional patent application No. 62/174,187, entitled “A CommonFramework for Finding Regions of Interest in Hematoxylin and Eosin (H&E)Stained Tissue Images and Quantifying Intratumor Cellular SpatialHeterogeneity in Multiplexed/Hyperplexed Fluorescence Tissue Images” andfiled on Jun. 11, 2015, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention pertains to digital pathology, and in particular,to a common framework for finding regions of interest in hematoxylin andeosin (H&E) stained tissue images and for quantifying intratumorcellular spatial heterogeneity in multiplexed/hyperplexed fluorescencetissue images.

2. Description of the Related Art

Digital pathology refers to the acquisition, storage and display ofhistologically stained tissue samples and is initially gaining tractionin niche applications such as: second-opinion telepathology, immunostaininterpretation, and intraoperative telepathology. Typically, a largevolume of patient data, consisting of 3-50 slides, is generated frombiopsy samples and is visually evaluated by a pathologist, under amicroscope, but with digital technology by viewing on a high-definitionmonitor. Because of the manual labor involved, the current workflowpractices are time consuming, error-prone and subjective.

Cancer is a heterogeneous disease. In hematoxylin and eosin (H&E)stained tissue images, heterogeneity is characterized by the presence ofvarious histological structures, such as carcinoma in situ, invasivecarcinoma, adipose tissue, blood vessels, and normal ducts. Oneprecision medicine approach to both intra- and inter-tumor heterogeneityis to sequence biopsied tissues and to identify a panel ofdisease-related genomic signatures, specifically for each patient andthe distinct regions of a single patient's tumor. However,genomic/epigenomic profiling requires either crushing up tissues ortaking multiple core samples from the tumor, yielding a time-consumingand low resolution understanding of the heterogeneity. Spatialinteractions between the various histological structures canprognosticate the disease. For example, a tumor nest growing into(invading) blood vessels indicates an increased risk of metastasis.Accurate segmentation of histological structures can thus help build aspatial interaction map to facilitate precision medicine studiescombining protein, DNA and RNA biomarkers for deep molecular profiling.This spatial interaction map can also serve as an exploratory tool forpathologists or as a guide to micro-dissection for further molecularprofiling.

Histological structure segmentation is a very challenging task becausestructures such as normal ducts and carcinoma in situ have well-definedboundaries, but many others, such as invasive carcinoma and stroma, donot. Structural morphologies also vary significantly depending on tissueorigins (e.g., breast vs. lung), and tissue preparation and stainingpractices. Historically, biomedical image analysis literature hasfocused on segmenting nuclei, since nuclei are building blocks for allhigher level tissue structures. More recent methods have expanded tosegmenting other histological structures, such as the glands in prostateand breast tissue images, with approaches based on nuclei-lumenassociation, region growth, region-based active contour in combinationwith Markov Random Field, and deep learning. Some other approachesinvolve engineering disease- and organ-specific extractors to facilitateanalysis of publicly available datasets, such as MITOS (mitotic figures)and GlaS (glands). For example, a typical gland segmentation strategymay involve first identifying a lumen and then searching for thesurrounding epithelial layer of cells. However, this strategy isunlikely to work in the case of breast carcinoma in situ, where the ductlumens may be completely filled by tumor cells. A basic mathematicalfoundation has been developed for supervised segmentation of H&E images,but that foundation has not been tested on more than a couple ofexamples.

Moreover, for many malignancies, molecular and cellular heterogeneity isa prominent feature among tumors from different patients, betweendifferent sites of neoplasia in a single patient, and within a singletumor. Intratumor heterogeneity involves phenotypically distinct cancercell clonal subpopulations and other cell types that comprise the tumormicroenvironment (TME). These cancer cell clonal subpopulations andother cell types include local and bone marrow derived stromal stem andprogenitor cells, subclasses of immune inflammatory cells that areeither tumor promoting or tumor-killing, cancer associated fibroblasts,endothelial cells and pericytes. The TME can be viewed as an evolvingecosystem where cancer cells engage in heterotypic interactions withthese other cell types and use available resources to proliferate andsurvive. Consistent with this perspective, the spatial relationshipsamong the cell types within the TME (i.e., spatial heterogeneity) appearto be one of the main drivers of disease progression and therapyresistance. Thus, it is imperative to define the spatial heterogeneitywithin the TME to properly diagnose the specific disease sub-type andidentify the optimal course of therapy for individual patients.

To date, intratumor heterogeneity has been explored using three majorapproaches. The first approach is to take core samples from specificregions of tumors to measure population averages. Heterogeneity in thesamples is measured by analyzing multiple cores within the tumor using anumber of techniques, including whole exome sequencing, epigenetics,proteomics, and metabolomics. The second approach involves “single cellanalyses” using the above methods, RNASeq, imaging or flow cytometryafter separation of the cells from the tissue. The third approach usesthe spatial resolution of light microscope imaging to maintain spatialcontext, and is coupled with molecular-specific labels to measurebiomarkers in the cells in situ.

Spatial analysis using light microscope imaging facilitates analysis oflarge areas of tissue sections and/or multiple tumor microarray sectionsat the cellular and subcellular levels. Subcellular resolution, forexample, permits the identification of the activation state of specificbiomarkers (e.g. translocation of transcription factors into thenucleus). In addition, recent developments in mass spectrometry imagingpermit many cellular constituents to be measured across a tissue sectionbut at a lower resolution than optical microscopy.

Several light microscopy imaging platforms have been developed tocharacterize cellular biomarker expression levels within tumorsincluding transmitted light and fluorescence. Multivariate informationbased on fluorescence has been acquired from images of large area tissuesections and tissue microarrays (TMAs) based on DNA, RNA and proteinbiomarkers, usually from 1 up to 7 fluorescently labeled biomarkers inthe same sample (known as multiplexed fluorescence). Multiple commercialplatforms can now be used to acquire, process, segment and perform somebasic analysis of biomarker signal levels in tissue samples. Recently,platforms have been demonstrated that permit up to 60 fluorescentlylabeled antibodies and a few DNA or RNA hybridization probes to beacquired in an iterative cycle of labeling, imaging, and quenchingfluorescence. It is also now possible to “map” the location of specificcell types, states of cell activations, cell biomarker expression levelsand localizations, as well as extracellular constituents in tissuesections and TMAs.

A major challenge is to develop algorithms that can quantify key spatialrelationships (interactions, and lack thereof) within the TME, based onpanels of biomarkers. Initial efforts in measuring heterogeneity intissue sections applied diversity metrics from ecological studies, suchas Shannon entropy and Rao's quadratic entropy. However, these methodshave not been adapted for multiplexed (up to 7 biomarkers) orhyperplexed (>7 biomarkers) immunofluorescence (IF) data. Other methodsthat account for high dimensional data may not have sophisticated cellphenotyping methods, allowing each biomarker to be only “on” or “off”.Furthermore, few of these methods incorporate the spatial relationshipsbetween biomarker patterns in their heterogeneity scores. Indeed, thespatial organization of the TME has been hypothesized to be an importantdiagnostic biomarker in addition to the expression levels of selectedbiomarkers from cancer and non-cancer cells.

Other heterogeneity characterization methods have: (i) incorporatedspatial information through region of interest sampling without usingnetwork-based approaches or taking advantage of multiplexed, (ii)analyzed linear relationships between biomarkers inmultiplexed/hyperplexed IF data without considering nonlinearassociations or spatial information, and (iii) have characterizedmultiplexed cell phenotype associations without any characterization ofthe underlying spatial organization within the tumor. In addition, mostother methods report intra-tumor heterogeneity as a single score, thuspotentially mapping two spatially different organizations of the TMEsincorrectly to the same score.

There is thus room for improvement in the fields of segmenting H&Eimages and quantifying intratumor cellular spatial heterogeneity inmultiplexed/hyperplexed fluorescence tissue images.

SUMMARY OF THE INVENTION

In one embodiment, a method of identifying regions of interest in an H&Estained tissue image is provided. The method includes receiving imagedata representing the H&E stained tissue image, quantifying localspatial statistics for the H&E stained tissue image based on thereceived image data, identifying histological structures within the H&Estained tissue image based on the local spatial statistics, andgenerating a segmented H&E stained tissue image using the received imagedata and the identified histological structures.

In another embodiment, a non-transitory computer readable medium isprovided that stores one or more programs, including instructions, whichwhen executed by a computer, causes the computer to perform the methodjust described.

In yet another embodiment, a computerized system for identifying regionsof interest in an H&E stained tissue image is provided. The systemincludes a processing apparatus, wherein the processing apparatusincludes: (i) a quantifying component configured for quantifying localspatial statistics for the H&E stained tissue image based on receivedimage data representing the H&E stained tissue image, (ii) anidentifying component configured for identifying histological structureswithin the H&E stained tissue image based on the local spatialstatistics, and (iii) a segmented tissue image generating componentconfigured for generating a segmented H&E stained tissue image using thereceived image data and the identified histological structures.

In still another embodiment, a method of quantifying intratumor cellularspatial heterogeneity in fluorescence tissue images is provided. Themethod includes receiving image data representing a number offluorescence tissue images, performing cellular segmentation on thereceived image data to identify a plurality of cells of the number offluorescence tissue images, assigning each of the cells to one of aplurality of predetermined biomarker intensity patterns, quantifyingspatial statistics for the number of fluorescence tissue images based onthe assigned predetermined biomarker intensity patterns, and generatinga visual representation of the quantified spatial statistics.

In another embodiment, a non-transitory computer readable medium isprovided that stores one or more programs, including instructions, whichwhen executed by a computer, causes the computer to perform the methodjust described.

In yet another embodiment, a computerized system for quantifyingintratumor cellular spatial heterogeneity in fluorescence tissue imagesis provided. The system includes a processing apparatus, wherein theprocessing apparatus includes: (i) a cellular segmentation componentconfigured for performing cellular segmentation on image datarepresenting a number of fluorescence tissue images to identify aplurality of cells of the number of fluorescence tissue images, (ii) anassigning component configured for assigning each of the cells to one ofa plurality of predetermined biomarker intensity patterns, (iii) aquantifying component for quantifying spatial statistics for the numberof fluorescence tissue images based on the assigned predeterminedbiomarker intensity patterns, and (iv) a visual representationgenerating component for generating a visual representation of thequantified spatial statistics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sample H&E stained image;

FIG. 2 shows the H&E image of FIG. 1 transformed into H&E hue spaceshown as a heat map (left) and an angular histogram (right);

FIG. 3 is a flowchart showing a first segmentation method according toan aspect of the disclosed concepts;

FIG. 4 is a flowchart showing a second segmentation method according toan aspect of the disclosed concepts;

FIG. 5 is a flowchart showing a method of establishing a set of dominantbiomarker intensity patterns according to an aspect of the disclosedconcepts;

FIG. 6 shows biomarker intensity distribution graphs with vertical linesdrawn to show two different regimes L1 and L2 for exemplary biomarkersemployed in the method described herein;

FIG. 7 shows pattern dictionaries learned separately for the twobiomarker intensity regimes L1 and L2 shown in FIG. 6;

FIG. 8 shows a 3D representation of the biomarker data from the cellularpopulation in the L1 regime with each cell phenotyped to belong to one,and only one, pattern in the dictionary and thus shown in a distinctcolor;

FIG. 9 illustrates the determination of the optimal size of the patterndictionaries for biomarker intensity regimes L1 and L2;

FIG. 10 illustrates consolidating the pattern dictionaries of regimes L1and L2 into one;

FIG. 11 is a flowchart showing the steps of a method for quantifyingspatial heterogeneity of multiplexed/high perplexed fluorescence tissueimages according to an exemplary embodiment;

FIG. 12 shows a schematic representation the predetermined dominantbiomarker intensity patterns employed according to an exemplaryembodiment;

FIG. 13 shows a cell spatial dependency image according to an exemplaryembodiment;

FIG. 14 shows a PMI map according to an exemplary embodiment;

FIGS. 15-17 show exemplary cell spatial dependency images and PMI maps;

FIG. 18 is a schematic representation of a system for implementing themethodologies for segmenting H&E images described herein; and

FIG. 19 is a schematic representation of a system for implementing themethodology for quantifying intratumor spatial heterogeneity asdescribed herein.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As used herein, the singular form of “a”, “an”, and “the” include pluralreferences unless the context clearly dictates otherwise.

As used herein, the statement that two or more parts or elements are“coupled” shall mean that the parts are joined or operate togethereither directly or indirectly, i.e., through one or more intermediateparts or elements, so long as a link occurs.

As used herein, the term “number” shall mean one or an integer greaterthan one (i.e., a plurality).

As used herein, the terms “component” and “system” are intended to referto a computer related entity, either hardware, a combination of hardwareand software, software, or software in execution. For example, acomponent can be, but is not limited to being, a process running on aprocessor, a processor, an object, an executable, a thread of execution,a program, and/or a computer. By way of illustration, both anapplication running on a server and the server can be a component. Oneor more components can reside within a process and/or thread ofexecution, and a component can be localized on one computer and/ordistributed between two or more computers. While certain ways ofdisplaying information to users are shown and described herein withrespect to certain figures or graphs as screen or screenshots, thoseskilled in the relevant art will recognize that various otheralternatives can be employed. The screens or screenshots are storedand/or transmitted as display descriptions, as graphical userinterfaces, or by other methods of depicting information on a screen(whether personal computer, PDA, mobile telephone, or other suitabledevice, for example) where the layout and information or content to bedisplayed on the page is stored in memory, database, or another storagefacility. The screens or screenshots may also be printed as desired.

As used herein, the term “superpixel” shall mean a coherent patch orgroup of pixels with similar image statistics.

Directional phrases used herein, such as, for example and withoutlimitation, top, bottom, left, right, upper, lower, front, back, andderivatives thereof, relate to the orientation of the elements shown inthe drawings and are not limiting upon the claims unless expresslyrecited therein.

A. Segmenting H & E Stained Tissue Images

A first aspect of the disclosed concepts focuses on improving thefunction and operation of (e.g., with improved processing capabilities)digital pathology systems and, in particular, on segmenting histologicalstructures in H&E stained images of tissues, such as breast tissues,e.g. invasive carcinoma, carcinoma in situ, atypical and normal ducts,adipose tissue, and/or lymphocytes. The present inventors hypothesizedthat spatial image statistics present discriminative fingerprints forsegmenting a broad class of histological structures. This aspect of thedisclosed concepts, described in greater detail herein, provides twograph-theoretic segmentation methods that each rely on characterizinglocal spatial statistics.

In the first method, each node in the graph corresponds to a pixel inthe image, and the edges correspond to the strength with which two nodesbelong to the same group. The edge strength is determined by measuringpairwise pixel statistics, in the form of bivariate von Mises mixturedistributions, in an opponent color space built to enhance theseparation between pink and purple stains in H&E images. Spectralmethods are used to partition the graph. The first method is expected tobe more successful in segmenting structures with well-defined boundaries(e.g., adipose tissues and blood vessels).

The second method is conveniently designed to extract histologicalstructures that have amorphous spatial extent (e.g., a tumor nest). Inthis formulation, putative nuclei centers become the nodes of a graphformed to capture the spatial distribution of the nuclei in H&E images.By applying data-driven thresholds on inter-nuclei spatial distances,the network is partitioned into homogeneous image patches.

The two segmentation methods described herein have two common elements,namely opponent color representation and appearance normalization, eachof which is described in detail below. The segmentation methods differin how they capture image statistics and embed them into graphpartitioning strategies. These aspects of the methods will be describedseparately herein.

When the known standard opponent-color (with red-green, yellow-blue asopponent color axes) hue-saturation-brightness (HSV) transformation isapplied to red-green-blue (RGB) images from H&E, the pink and purplecolor ranges are restricted to the blue-red quadrant of the color wheel.A goal of this aspect of the disclosed concepts is to enhance theseparation between pink and purple colors so that the downstream spatialanalysis pipeline is more robust. For this, the construction of a colorspace is optimized to opponently place the pink and purple colors.Specifically, in the exemplary implementation, an expert was allowed toselect a bag of pink and purple pixels. Then, singular valuedecomposition was performed on this collection of data to obtain anorthogonal projection matrix of size 3×3. This aspect of the disclosedconcepts provides a specific interpretation to the projectedcoordinates, similar to the opponent space HSV. In particular, theprojection onto the first singular vector (enforced to have non-negativevalues) yields an H&E-brightness value b. The two remaining projectedcoordinates, c2 and c3, form a complex plane in which H&E-saturations=√{square root over (c₂ ²+c₃ ²)} and H&E-hue θ=tan⁻¹(c₂+ic₃). From thisconstruction, the hue values of purple and pink pixels are expected tobe maximally separated in the complex color plane. For illustration, itis noted that the angular difference in the mean hue values of the pinkand purple pixels in FIG. 1, which is a sample H&E stained image, is 1:7radians, as shown in FIG. 2, which is the H&E image of FIG. 1transformed into H&E hue space shown as a heat map (left) and an angularhistogram (right). This spread is more than the value of ≈0:4 radiansobtained from the standard HSV opponent color space. Hue value isunstable when the saturation is low. This is true for pixels mapped tothe origin of the complex plane (c₂; c₃≈0). In the standard HSVrepresentation, all white pixels will have low saturation values andhence unstable hue angles. Note that white pixels can form a significantportion of an H&E image because of adipose tissue, lumen, tissue tears,and shrinkages. In the opponent color representation of this aspect ofthe disclosed concepts, by learning the rotation matrix from anexpert-selected pink/purple pixel bag, white pixels are able to be givenhigher saturation values and more stable hue angles. However, there willbe a population of pixels with low saturation values (say <0:005) thatmap to the origin of the complex plane. This population is empiricallyestimated to be around 0:3% for the H&E images of size 2K×2K that wereused.

In addition, any inconsistencies in sectioning, staining, and imagingresult in variation in color appearance of H&E images. Thus, in theexemplary embodiment, the data is normalized. Previous normalizationmethods have utilized stain vector estimation methods such asnon-negative matrix factorization. These methods were found to beineffective for this aspect of the disclosed concepts because the colordistributions for some images are very skewed toward mostly purple ormostly pink. The present inventors hypothesized that the colorappearance of two images is similar if their color statistics match.However, matching the statistics of the whole pixel population of thesource and target images can result in unintended artifacts. Forexample, if the source image has mostly pink pixels (stroma) and thetarget image has mostly purple pixels (invasive carcinoma), thenmatching the source image statistics to the target image statistics willturn many pink pixels in the source image to purple and mistakenlychange the cellular component identity of those pixels from stroma tonuclei. To address this issue, the following three classes of pixels arefirst identified: pink (eosin), purple (hematoxylin), and white (e.g.,fat, shrinkage), and the statistics are matched separately for each ofthese classes. To identify the three classes, H&E images are convertedinto H&E-hue, H&E-saturation, and H&E-brightness channels as discussed.The H&E-hue space is angular and given the separation between pink,purple, and white pixel clouds in this space, the hue values are modeledwith a mixture of univariate von Mises distributions. Univariate vonMises distribution for angular statistics is the equivalent counterpartof the univariate normal distribution for linear statistics. The vonMises distribution is characterized by two parameters, a mean −π<μ≤π anda concentration parameter κ>0, and is given by: ƒ(x)={2κI₀(κ)}⁻¹ exp κcos(x −μ), where I₀(κ) is the modified Bessel function of the first kindwith order 0. A mixture of K univariate von Mises distributions is givenby Σ_(k=1) ^(K)m_(k)ƒ_(k)(x|μ_(k),κ_(k)), where m_(k)'s are the priorprobabilities and μ_(k)'s, κ_(k)'s are the means and concentrationparameters. To explicitly account for pixels with low saturation valuesand unstable hue angles, a uniform angular noise is added as anadditional mixture component whose prior probability is approximately0.3%. The parameters of univariate von Mises mixture can be found usingan expectation-maximization (EM) algorithm. The statistics of adistribution can be characterized by an infinite set of moments.However, for analytical convenience, in the exemplary embodiment,moments are computed only up to the fourth order (mean, standarddeviation, skewness, kurtosis). In each channel, the moments of eachpixel class from the source image are matched to the target image. Forexample, the moments of purple pixels in the source image are matched tothe moments of purple pixels in the target image in all three channels.After normalizing the statistics in the H&E opponent color space, theresulting pixel values are converted into the RGB space (to createnormalized RGB data) using the inverse of the rotation matrix describedabove.

Having described the two common elements of the two segmentationmethods, namely opponent color representation and appearancenormalization, the remainder of each segmentation method will now bedescribed in detail. In each of the segmentation methods, normalizedimage data serves as inputs. In particular, normalized H&E-hue data isused as inputs in the first method, and normalized RGB data is used asinputs in the second method.

With regard to the first method, normal breast tissues have large areasof pink stained connective tissue (CT) surrounding small areas of ducts,each of which is an assembly of cells. The nuclei of these cells will bestained dark purple, while the cytoplasm that surrounds the nucleiexhibits a mixture of pink and purple, since the purple stain from thenuclei can spill over to the cytoplasm. Statistically speaking, if onewere to stand on any of these nuclei, one would expect to be surroundedby purple pixels denoting the nuclei and pink-purple pixels denoting thecytoplasm. If these cells assemble into a duct structure, then in agiven neighborhood of each cell, other cells exhibiting similarproperties should be found. On the other hand, if one were stand on afibroblast cell nucleus, which is found usually scattered in theconnective tissue, one would find mostly pink pixels in itsneighborhood. With the assumption that the statistical associationwithin a structure such as ducts is higher than across its boundaries,ducts should be able to be segmented while ignoring the fibroblast cellsscattered among the connective tissue.

Using a mixture univariate von Mises distributions, the image pixels canbe separated into pink, purple and white classes, but this isinsufficient to delineate histological structures, such as theglands/ducts, because such structures contain pixels from all threeclasses. In this aspect of the disclosed concepts, in order to segmentthese structures, it is assumed that the statistical association withina structure such as a duct is higher than across its boundaries, andthis statistical association is modeled, according to this aspect of thedisclosed concepts, using a mixture of bivariate von Misesdistributions. Since the H&E-hue is an angular variable, the jointdistribution P(A, B) of hue values from two neighboring pixels lies on atorus. This joint density is modeled as a mixture of bivariate von Misesdistributions. Let the values of pixel A and B in H&E-hue space be φ andψ, respectively. The bivariate distribution of two angular variables,−π<φ≤π and −π<ψ≤π is:

ƒ_(c)(φ,ψ)=C _(c)exp[K ₁ cos(φ+μ)+κ₂ cos(ψ−ν)−κ₃ cos(φ−μ−ψ+ν)]

where μ, υ are the means and κ₁, κ₂>0 are the concentrations of φ, ψ,respectively, κ₃ is the correlation coefficient and C_(c) is thenormalizing constant. The full bivariate von Mises model has 8parameters, but a reduced 5-parameter cosine model with positiveinteraction is used in the exemplary embodiment. The marginal densityis: ƒ_(c)(ψ)=c_(c) 2πI₀(κ₁₃)(ψ) exp{κ₂ cos(ψ−ν)}. The value of κ₃decides whether the distribution is unimodal or bimodal. In particular,the joint density is unimodal if κ₃<κ₁κ₂/(κ₁+κ₂) and it is bimodal ifκ₃>κ₁κ₂/(κ₁+κ₂) when κ₁>κ₃>0 and κ₂>κ₃>0.

When the values of neighboring pixels of the H&E image in the H&E-huespace are considered, there are at most six possibilities for the masseson the torus: purple-purple, pink-pink, white-white, and the threedifferent pairwise interactions. To model this joint distribution, amixture of six unimodal bivariate von Mises distributions is used. Amixture model of K bivariate von Mises distributions can beparameterized by: ƒ_(c)(φ,ψ)=Σ_(i=1)^(K)m_(i)ƒ_(i)(φ,ψ|μ_(i),ν_(i),κ_(1i),κ_(2i),κ_(3i)). The initial valuesof μ_(i), ν_(i), κ_(1i), and κ_(2i) are generated from the mixture ofunivariate von Mises for all the pixels in the image. The concentrationparameters κ_(1i), and κ_(2i) and the correlation parameter κ_(3i)satisfy the unimodality conditions for ƒ_(i). κ_(3i) is constrained tohave values between −1 and 1 to avoid distortion to the ellipticalpatterns (observed in sampled data). Together with the aboveconstraints, the parameters of the mixture are estimated by an EMalgorithm. Since there are at most six components of the mixture modelas reasoned above, an explicit model selection step is not undertakenfor the mixture model. If the H&E image lacks any one of the three basiccolors, purple, pink, and white, the prior probabilities or mixingproportions of clusters related to that color will be close to 0.

Consider modeling the statistical dependencies between hue angles ofneighboring pixels in the H&E opponent color space. If the jointprobabilities are used as a measure of statistical association, it maybe found that the pink-pink pixel pair in the connective tissue has ahigher probability than a purple-purple pixel pair inside a duct or apink-purple pixel pair across the CT-duct boundary. However, because ofthe overabundance of pink in some H&E images, the combination ofpink-purple pixel pairs across the CT-duct boundary may have anequivalent or even higher probability than a purple-purple pixel pairinside the duct. A pink-pink pair may have the highest joint probabilityand a purple-purple pair may have similar joint probability to apurple-pink pair. In other words, the joint probability might not besufficient to detect correct boundaries. This can be improved by the useof mutual information (MI) to correct for relative abundance. To computeMI, a number of pixel pairs (A,B) with features {right arrow over(ƒ_(A))} and {right arrow over (ƒ_(B))} (e.g. H&E-hue angles) areselected randomly from all locations of the image and with distancesless than a threshold. The joint probability of features of A and B at adistanced apart is denoted as p(A, B; d). The overall joint probabilityis defined as:

${P\left( {A,B} \right)} = {\frac{1}{Z}{\sum_{d = d_{0}}^{\infty}{{w(d)}{{p\left( {A,{B;d}} \right)}.}}}}$

The value of d depends on the parameter σ, in particular d=2+2|r| wherer˜N(0, σ). A nucleus is ≈15 pixel in diameter at 10× magnification.Since the segmentation algorithm targets assembly of nuclei, thedistances between pixel pairs sampled should cover at least the diameterof a nucleus. Hence, σ is set to 3. The pointwise mutual information(PMI) is calculated from the joint probability P(A,B) modeled by amixture of bivariate von Mises distribution and the marginalprobabilities P(A) and P(B) modeled by a mixture of univariate von Misesdistributions. In particular,

${P\; M\; {I_{\rho}\left( {A,B} \right)}} = {\log {\frac{{P\left( {A,B} \right)}^{\rho}}{{P(A)}{P(B)}}.}}$

In the exemplary embodiment, ρ=2 to normalize for the upper bound of

$\frac{{P\left( {A,B} \right)}^{\rho}}{{P(A)}{P(B)}}.$

Furthermore, an affinity function is defined from PMI to indicate thelikelihood of grouping two pixels into the same histological structure.The affinity matrix W with elements w_(i,j) denotes similarity betweenpixels i and j:

$w_{i,j} = {e^{{PMI}_{\rho}({\overset{\rightarrow}{f_{i}},\overset{\rightarrow}{f_{j}}})}.}$

The affinity function is used as an input to a standard spectral graphsegmentation method, such as that described in Arbelaez, P. et al.,“Contour Detection and Hierarchical Image Segmentation”, IEEE TPAMI,33(5), 898-916 (20122) that has been the state-of-the-art for segmentingnatural images. From the affinity matrix W, eigenpairs {right arrow over(ν)},λ of the generalized system are found: (D −W){right arrow over(ν)}=λD{right arrow over (ν)}. Dominant eigenvector maps (smalleigenvalues) indicate boundary locations of potential histologicalstructures. As is well known, no single eigenvector will be capable ofcapturing all possible boundaries in complex images. Hence, the usualpractice is to calculate an edge strength map from oriented spatialderivative of a large number of dominant eigenvectors. A post-processingstep is used to eliminate spurious boundary pixels.

FIG. 3 is a flowchart that summarizes the first segmentation method asjust described in detail. The method begins at step 5, whereinnormalized H&E-hue data for a subject slide is received. Next, at step10, the joint distribution of the normalized H&E-hue values between aplurality of neighboring pixels in the H&E-hue data is estimated. Then,at step 15, the PMI for the normalized H&E-hue data is calculated basedon the estimated joint distribution. At step 20, an affinity function isdefined from the calculated PMI. Finally, at step 25, tissues in thesubject slide are segmented using the affinity function and a spectralgraph segmentation method (also known as spectral clustering).

With regard to the second segmentation method, local spatial statisticsvary between the various histological structures in breast tissues. Forexample, the clump of cells in ductal carcinoma in situ tends toaggregate with their boundaries in close proximity of each other,because the in situ tumor is growing but is confined within ducts. Onthe other hand, epithelial cells in invasive carcinoma are spatially farapart. They are also growing, but can freely infiltrate into and throughthe breast stroma, no longer confined to ducts. Local statistics ofnormal ducts is more ordered, in particular, normal epithelial (inner)and myoepithelial cells (outer) form two layers surrounding a cavity(lumen).

For adipose tissue, the nuclei are small and to one side of the cells.The majority of adipose tissue consists of fat droplets. The presentinventors hypothesized that different histological structures havedifferent distributions of inter-nuclei distances (local statistics). Asdescribed below, the second segmentation method of this aspect of thedisclosed concepts is based on this hypothesis.

Nuclei segmentation in histopathological and cytopathological images isan extensively researched problem. However, the close proximity ofepithelial cells and the prevalence of mitotic figures (dividing cells)in breast cancer make it difficult to accurately detect nuclearboundaries, which is even difficult for human eye. To avoid this issue,in the second segmentation method, putative nuclei locations areidentified in the form of superpixels, which will approximatelyrepresent nuclei, and a graph connecting superpixels is constructed toobtain neighborhood and distance information for each superpixel pair.More specifically, in the exemplary embodiment, in order to generatesuperpixels from H&E images, first, the pixel colors are normalized asdescribed above. Then, the algorithm proposed in Tosun, A. B. andGunduz-Demir, C., “Graph Run-length Matrices for Histopathological ImageSegmentation”, IEEE TMI, 30(3), 721-732 (2011), is performed to fitcircular shaped superpixels. Briefly, this algorithm first clusterspixels into three classes based on intensities using k-means algorithm,in which cluster centers are determined over randomly selected trainingimages using principal component analysis. These three classesrepresents purple, pink, and white regions which correspond to nuclei,stroma and lumen/white regions respectively. This algorithm then fitscircular superpixels into clustered pixels for nuclei, stroma andlumen/white components. After superpixel decomposition, a Delaunaytriangulation is formed based on center coordinates of superpixels todetermine the neighborhood of each superpixel. Having the distanceinformation for each superpixel pair, final segmentation of histologicalstructures is achieved by partitioning this graph in a greedy manner andapplying merging rules for specific types of segments, which is detailedin following sections. Although the proposed method is motivated by theinter-nuclei distance distribution, superpixels pairs from both purpleand white pixel classes are considered to account for complexhistological structures such as ducts, blood vessels and adiposetissues. For example, normal duct has purple nuclei forming two celllayers surrounding a white lumen area. On the other hand, the stroma(pink) class is considered as the background and is not included ingraph partitioning step.

More specifically, each superpixel is considered a node in a graph andthe connectivity of the graph is determined by a distance threshold. Foreach class, the pairwise distance between a superpixel center and itsnearest 15 neighbors (identified by the Delaunay triangulation) iscalculated. The distance threshold τ is set to be proportional to themedian value (δ) of the distance distribution. The proportionalityconstant is set to maximize the performance of the algorithm for theentire database. After building the superpixel graph, a greedy connectedcomponent analysis algorithm is used to cluster superpixels into labeledsegments. In the exemplary embodiment, the largest 15 segments in termsof tissue area are selected. Since tissue images in the exemplaryembodiment are of size 2K×2K, only a handful of ducts, tumor nests, fatdroplets are expected in any given image. At this point, two sets oflabeled segments have been obtained from the purple and the whitesuperpixels.

To merge purple segments and white segments into the final histologicalstructures, a few simple rules are followed to make sure that importantstructures formed by nuclei clusters are not missed. If a white segmentis completely covered by a purple segment, the whole purple area takesthe label of the purple segment. If a white segment overlaps with apurple segment, regardless of overlapping area, the overlapping parttakes the label of the purple segment and the non-overlapping part takesthe label of the white segment. If a purple segment is completelycovered by a white segment, the purple area takes the purple segment'slabel and the remaining white area retains the white segment's label.This is to make sure that a nuclei clump residing within a vessel is notmissed. After merging purple and white segments, the remaining unlabeledarea is considered as background or stroma.

FIG. 4 is a flowchart that summarizes the second segmentation method asjust described in detail. The method begins at step 30, whereinnormalized RGB data for a subject slide is received. Next, at step 35,putative nuclei locations are identified in the form of superpixels fromthe RGB data. Then, at step 40, a superpixel graph is built based on thepairwise distance between each superpixel and a number of its nearestneighbors. Next, at step 45, using the superpixel graph, the superpixelsare clustered or grouped into labeled segments. Finally, at step 50, thelabeled segments are merged into final histological structures. Thedetermined final histological structures are then used to segment thesubject slide (i.e., create an image wherein the subject slide issegmented).

B. Quantifying Intratumor Spatial Heterogeneity

As described in greater detail herein, another aspect of the disclosedconcepts provides improvements in the function and operation of (e.g.,improved processing) digital pathology systems. In particular, thisaspect provides a method for quantifying intratumor spatialheterogeneity that can work with single biomarker, multiplexed, orhyperplexed immunofluorescence (IF) data. The method is holistic in itsapproach, using both the expression and spatial information of an entiretumor tissue section and/or spot in a TMA to characterize spatialassociations. In the exemplary embodiment described in detail herein,the method generates a two-dimensional heterogeneity map to explicitlyelucidate spatial associations of both major and minor sub-populations.It is believed that the characterization of intratumor spatialheterogeneity will be an important diagnostic biomarker for cancerprogression, proliferation, and response to therapy, and thus the methodand system of this aspect of the disclosed concepts will be a valuablediagnostic and treatment tool.

According to this aspect of the disclosed concepts, a predetermined setof particular biomarkers is employed to quantify spatial heterogeneityin multiplexed/hyperplexed fluorescence tissue images. For illustrativepurposes, this aspect of the disclosed concepts is demonstrated hereinin a non-limiting exemplary embodiment wherein spatial heterogeneity isquantified using three breast cancer biomarkers (estrogen receptor (ER),human epidermal growth factor 2 (HER2), and progesterone receptor (PR))combined with biomarkers for segmentation including the nucleus, plasmamembrane, cytoplasm and epithelial cells. It will be understood,however, that this aspect of the disclosed concepts may be used withdifferent and/or additional biomarkers. In addition, it will also beunderstood that the impact of this aspect of the disclosed concepts,which uses pointwise mutual information (PMI) to quantify spatialintratumor heterogeneity, can be extended beyond the particularexemplary embodiments described herein. For example, and withoutlimitation, this aspect of the disclosed concepts may be extended to theanalysis of whole-slide IF images, labeled with increasing numbers ofcancer and stromal biomarkers.

Furthermore, this aspect of the disclosed concepts employs apredetermined set of dominant biomarker intensity patterns (based on thepredetermined set of particular biomarkers being used), also referred toherein as phenotypes, to measure and quantify cellular spatialheterogeneity. Thus, as an initial matter, a non-limiting exemplarymethod of establishing the set of dominant biomarker intensity patternswill first be described below with reference to FIG. 5. Thereafter, themanner in which the set of dominant biomarker intensity patterns isemployed to quantify spatial heterogeneity is described.

Referring to FIG. 5, first, at step 105, a set of digital control slidesis obtained wherein each control slide includes a digital biomarkerimage which has been cell segmented (i.e., a cell segmentation methodhas been performed thereon). In the exemplary embodiment describedherein for illustrative purposes, at least the three biomarkersdescribed above (ER, PR and HER2) were used in the generation of thebiomarker images of the control slides. Next, at step 110,immunofluorescence (IF) data is generated for the set of control slides.In particular, the IF data is generated in step 110 by obtaining, foreach biomarker image, the intensity level of each of the predeterminedbiomarkers for each segmented cell in the biomarker image. Thus, as willbe appreciated, the IF data will comprise biomarker intensity level datafor each segmented cell of each biomarker image of the control slides.

Next, at step 115, the cells from the IF data are segregated into twopartitions (using thresholds as described below) based on thedistribution of signal intensity for each biomarker, under theassumption that signal intensity indicates true biomarker expression.FIG. 6 shows biomarker intensity distribution graphs for each of theexemplary biomarkers (ER, PR, HER2). Each of the log-occurrencedistributions shown in FIG. 6 may be modeled by two or more linearequations. The notch where these two different models would meet is setto be the threshold for that particular biomarker channel, and is drawnas vertical lines in the biomarker intensity distribution graphs of FIG.6. For any given cell, if one or more of its biomarker intensities isabove threshold, that cell is classified as level 1 (L1). If all of thebiomarker intensities for any given cell are below the thresholds intheir corresponding biomarker channels, that cell is classified as level2 (L2). These two partitions can be interpreted in terms of theirsignal-to-noise ratio, where L1 has a higher signal-to-noise ratio andL2 has a lower signal-to-noise ratio, in comparison. Each partition ofcells is used to learn its own set of biomarker intensity patterns. Thisapproach seems particularly judicious, given that the distribution ofpattern coefficients for L1 and L2 data have different Gaussianity ingeneral. As shown in FIG. 6, the studied biomarker intensities havelong-tailed distributions, so a log-intensity representation is chosento derive a numerically stable pattern recognition algorithm.

Next, at step 120 of FIG. 5, a set of dominant biomarker intensitypatterns, also referred to herein as phenotypes, is learned from thepartitioned IF data as follows. First, for each partition of the IFdata, L1 and L2, a sparse signal representation is derived as seen inFIG. 7. More specifically, referring to FIG. 7, a given data matrix X,where the columns represent each cell in the IF data, and the rowsrepresent the log biomarker intensities of each cell (top to bottom, ER,HER2, PR, respectively), can be approximated by the product of matricesD and W. D represents a dictionary of potential biomarker intensitypatterns learned from the ensemble of cells in the dataset X, where eachcolumn represents one of the patterns learned from the data, and eachrow represents the respective biomarker intensities of each pattern. Wis a sparse matrix, which phenotypes each cell in X to a specificpattern in D with a particular scaling coefficient. Thus, each cell(column in W) is represented by only one cell phenotype, whichcorresponds to the biomarker pattern (column in D) where the sparse codelies. The color spectrum for each matrix varies from one color, forexample blue (low intensity) to another color, for example yellow (highintensity). Matrix DW is displayed to portray the similarity between theactual data matrix and its reconstruction. By viewing matrices X and DW,which are column sorted by the dictionary element they have the mostconsensus with, it can be observed that each of the biomarker intensitypatterns is present in the data. The benefit of this reconstruction ofthe data is the ability to represent a large array of cell-level datawith a small number of interpretable biomarker intensity patterns,describing highly clustered clouds inherent to the dataset as shown inFIG. 8. Each cell in the 3D log biomarker intensity space is color codedby its phenotype. The reconstruction error of the linear representationof a given dataset X into dictionary D and dictionary coefficient matrixW is highly dependent on the dimensionality of D, i.e., the number ofpatterns that will be used to describe the dataset X.

In order to choose the ideal dimensionality of D, a ten-fold crossvalidation of the data reconstruction is performed as shown in FIG. 9.As is typical in these analyses, it is noted that as the dimensionalityincreases, reconstruction error and the variance of the error decrease,until a certain point where the error variance begins to increase withdimensionality. In the exemplary embodiment, it has been found that adictionary size of 11 patterns optimizes both reconstruction error andvariance of the error, for both data partitions, L1 and L2. Havinglearned a set of 11 patterns for each non-overlapping partition of thedata L1 and L2, the two dictionaries could be merged into a large singledictionary of biomarker intensity patterns that can describe the entiredataset. However, since these patterns were learned separately frompartitions deriving from the same dataset, captured under the sameexperimental conditions, it was noted that there were some redundanciesbetween the dictionary learned from L1 data and the dictionary learnedfrom L2 data. Thus, in the exemplary embodiment, k-means clustering wasused to consolidate the large 22 pattern dictionary (with 11 patternsfrom each partition) into a smaller final dictionary containing only theunique patterns discovered from approach described herein. FIG. 10 showsthe 11 patterns learned from L1 and the 11 patterns learned from L2.Each biomarker pattern is represented as a stem plot of its ER, HER2,and PR intensity, respectively. For convenience, the intensity patternsin the stem plots will be described as being high, medium, and low. Forexample, pattern 8 in the L1 dictionary (shown to the left) may bedescribed as ER high, HER2 medium, and PR low.

The results of k-means clustering, shown to the right in FIG. 10, resultin a final dictionary dimensionality of 8 biomarker intensity patterns.In the exemplary embodiment, the final dimensionality was chosen basedon the results of a silhouette criterion for clustering evaluation. Notethat one pattern was unique to partition L2, pattern 7 of the finalpattern set, with low ER expression, intermediate HER2 expression, andhigh PR expression. This demonstrates the value of partitioning the datainto two groups, L1 and L2, where patterns dominant in one partition,but not the other, may be elucidated.

Having described the exemplary methodology for learning a set ofdominant biomarker intensity patterns, the discussion will now shift tothe manner in which the set of dominant biomarker intensity patterns isemployed to quantify spatial heterogeneity. In particular, FIG. 11 is aflowchart showing the steps of a method for quantifying spatialheterogeneity of multiplexed/high perplexed fluorescence tissue imagesaccording to an exemplary embodiment.

Referring to FIG. 11, the method begins at step 125, wherein a numberdigital multiplexed fluorescence slides to be analyzed is obtained. Thenumber of slides obtained in step 125 may be a single slide, multipleslides from a single patient, or multiple slides for an entire patientcohort. As will be appreciated, the slide(s) obtained in step 125 willeach include a section of a tumor of interest, and will each be abiomarker image of that section. As noted elsewhere herein, thebiomarkers being used in the exemplary embodiment are ER, PR, and HER2.Next, at step 130, cell segmentation is performed on the digital slidedata of the subject slide(s). Any of a number of known or hereafterdeveloped suitable cell segmentation algorithms may be employed at step130. Then, at step 135, spatial location and biomarker intensity datafor each cell in the subject slide(s) is obtained. Next, at step 140,each cell of the subject slide(s) is assigned to one of thepredetermined dominant biomarker intensity patterns (i.e., one of thephenotypes) based on the biomarker intensity composition of the cell.FIG. 12 shows a schematic representation 160 of each of thepredetermined dominant biomarker intensity patterns, labeled 1-8. In theexemplary embodiment, each schematic representation 160 is provided in aunique color or colors so as to enable the schematic representations tobe readily distinguishable from one another. Next, at step 145, the cellassignments and the schematic representations shown in FIG. 12 are usedto generate a cell spatial dependency image which visually demonstratesthe heterogeneity of the subject tissue sample(s). FIG. 13 shows a cellspatial dependency image 165 according to one particular exemplaryembodiment of the disclosed concept. As seen in FIG. 13, cell spatialdependency image 165 shows spatial dependencies among the cells of thesubject slide(s) using the schematic representations 160. In theexemplary embodiment, cell spatial dependency image 165 records theprobabilities of the following cases: (i) if immune cells occur in thevicinity of cancer cells, (ii) if immune cells and cancer cells suppresseach other, and (iii) if immune cells and cancer cells are agnostic ofeach other. Cell spatial dependency image 165 is not meant to show anyparticular tissue structure.

Next, at step 150, a spatial network is constructed to describe theorganization of the dominant biomarker intensity patterns in the subjectslide(s). Then, at step 155, the heterogeneity of the subject slide (s)is quantitated by generating a PMI map for the slide(s) as describedherein. In the exemplary embodiment, steps 150 and 155 are performed asset forth below.

In order to represent the spatial organization of the biomarker patternsin the biomarker image (i.e., the tissue/tumor sample) of the subjectslide(s), a network is constructed for the subject slide(s). Theconstruction of spatial networks for tumor samples intrinsically couplescellular biomarker intensity data (in the nodes of the network) tospatial data (in the edges of the network). The assumptions in thenetwork construction are that cells have the ability to communicate withnearby cells up to a certain limit, e.g., up to 250 μm, and that theability for cells to communicate within that limit is dependent uponcellular distance. Therefore, the probability distribution in theexemplary embodiment is computed for the distance between a cell in thesubject slide and its 10-nearest neighbors. A hard limit was chosenbased on the median value of this distribution times 1.5 (to estimatethe standard deviation), where cells in the network were connected onlywithin this limit. Then, the edges between cells in the network areweighted by the distance between the adjacent cells.

Next, pointwise mutual information (PMI) is used to measure theassociation between each pair of biomarker patterns in the dictionary,and thus different cell phenotypes, for the subject slide(s). Thismetric captures general statistical association, both linear andnonlinear, where previous studies have used linear metrics such asSpearman's rho coefficient. Once PMI is computed for each pair ofbiomarker patterns, a measure of all associations in the data of thesubject slide is displayed in a PMI map. An exemplary PMI map 170 isshown in FIG. 14.

PMI map 170 describes relationships between different cell phenotypeswithin the microenvironment of the subject slide(s). In particular, theentries 172 in PMI map 170 indicate how frequently a particular spatialinteraction between two phenotypes (referenced by the row and columnnumber) occurs in the dataset when compared to the interactionspredicted by a random (or background) distribution over all phenotypes.Entries in a first color, such as red, denote a strong spatialassociation between phenotypes, while entries in a second color, such asblack, denote a lack of any co-localization (weak spatial associationbetween phenotypes). Other colors may be used to denote otherassociations. For example, PMI entries 172 colored in a third color,such as green, denote associations that are no better than a randomdistribution of cell phenotypes over the entire dataset. Additionally,PMI map 170 can portray anti-associations with entries 172 denoted in afourth color, such as blue (e.g., if phenotype 1 rarely occurs spatiallynear phenotype 3).

Thus, a PMI map 170 with strong diagonal entries and weak off-diagonalentries describes a globally heterogeneous but locally homogeneoustumor. An example of such a PMI map 170A is shown in FIG. 15. In thisexample, the associations in the diagonal entries for phenotypes 2, 4and 8 are strong. This implies that these phenotypes are spatiallyassociated with cells of the same phenotype, as shown by the compositionof the individual microdomains in the tumor sample image shown in FIG.15. On the contrary, a PMI map 170B with strong off-diagonal entries candescribe a tumor that is locally heterogeneous. An example of such a PMImap 170B is shown in FIG. 16. In this example, the associations betweenthe cellular phenotypes 1 and 6, the cellular phenotypes 2 and 4, andthe cellular phenotypes 3 and 8 are spatially localized. Furthermore,PMI map 170B shows only one association of phenotype 7 cells withitself. Exemplary PMI map 170C shown in FIG. 17 shows associationsbetween all phenotypes in the tumor image and hence PMI map 170C isthoroughly intermixed with colors. The benefit of PMI maps 170 overexisting measures is that the maps evoke a spatial relationship betweenphenotypes. They provide not only a summary of cellular composition, butan approximation of the tumor topology. For the sake of brevity, morecomplicated PMI map examples have not been included, but it will beunderstood that all PMI maps 170 are built off of these simpleinteractions.

In the exemplary embodiment, PMI for the subject slide(s) is calculatedas follows. Given a linear deconstruction of an IF dataset X, where eachcolumn of X is a cell x_(k), into an overcomplete dictionary D, whereeach column of D is a distinct pattern d_(i), and a sparse coding matrixW which assigns each cell to only a single biomarker intensity pattern,each cell is, as described herein (step 140) assigned to have aphenotype ƒ_(i) where i is the nonzero index in column w_(k) of W. Apotential pitfall of the algorithm is that high and low signal intensitycells can be assigned to the same cell phenotype. PMI between a pair ofbiomarker phenotypes (ƒ_(i), ƒ_(j)) for a given network or network setsis defined as:

${{P\; M\; {I_{s}\left( {f_{i},f_{j}} \right)}} = {\log \frac{P\left( {{f_{i}}_{s},f_{j_{s}}} \right)}{{P\left( f_{i_{t}} \right)}{P\left( f_{j_{t}} \right)}}}},$

where P(ƒ_(i) _(s) ) is the probability of phenotype ƒ_(i) occurring innetwork set s, and P(ƒ_(i) _(t) ) is the background probabilitydistribution of phenotype ƒ_(i) derived from the complete ensemble ofnetworks. Note that the background distributions are based on the entiredataset, in order to compare individual networks to the distribution oftissue slide as a whole. This construction is similar to theposition-specific scoring matrices (PSSM) for either DNA or proteinsequences, where the background distributions denote the probability offinding any particular nucleotide or amino acid over the dataset ofsequences, for any given position. A PMI map consists of the PMI scorefor every possible pair of patterns in the vocabulary for a givennetwork set s. While we advocate the interpretation of thetwo-dimensional PMI map for a thorough understanding of heterogeneity,we also derive a one-dimensional heterogeneity score value from the PMImap, for convenience of the reader interested in comparing with otherone-dimensional scores in the literature. The information-deficientone-dimensional heterogeneity score is defined as:

${{HET}_{P\; M\; I_{s}} = {\sum_{i,j}{{\log \frac{P\left( {{f_{i}}_{s},f_{j_{s}}} \right)}{{P\left( f_{i_{t}} \right)}{P\left( f_{j_{t}} \right)}}}}}},$

where higher scores denote a larger difference from the backgrounddistribution. The one-dimensional scores can incorrectly map twospatially different organizations of the TMEs, as seen by their PMImaps, to the same scale.

After computing PMI map 170 for the subject slide(s) and identifyingsignificant interactions or interaction motifs, it is necessary tointerrogate the cells which contributed to this significant association.A significant interaction would be considered when the PMI value isclose to ±1. PMI values close to 1 signify that this particular spatialinteraction of biomarker patterns occurs more frequently than isobserved in the background distribution. PMI values close to −1signifies that when one pattern is observed in the network, that theother pattern is found to be observed less frequently than expected fromthe background distribution. PMI values close to zero signifyinteractions that may adequately be described by the backgrounddistribution.

C. System Implementations

FIG. 18 is a schematic diagram of an exemplary system digital pathology200 in which the H&E stained tissue image segmentation methodologiesdescribed herein may be implemented. As seen in FIG. 18, system 200 is acomputing device structured to receive digital image data representativeof H&E stained tissue images and process those images as describedherein. System 200 may be, for example and without limitation, a PC, alaptop computer, a tablet computer, a smartphone, or any other suitabledevice structured to perform the functionality described herein. System200 includes an input apparatus 202 (such as a keyboard), a display 204(such as an LCD), and a processing apparatus 206. A user is able toprovide input into processing apparatus 206 using input apparatus 202,and processing apparatus 206 provides output signals to display 204 toenable display 204 to display information to the user (such as segmentedtissue images) as described in detail herein. Processing apparatus 206comprises a processor and a memory. The processor may be, for exampleand without limitation, a microprocessor (μP), a microcontroller, orsome other suitable processing device, that interfaces with the memory.The memory can be any one or more of a variety of types of internaland/or external storage media such as, without limitation, RAM, ROM,EPROM(s), EEPROM(s), FLASH, and the like that provide a storageregister, i.e., a machine readable medium, for data storage such as inthe fashion of an internal storage area of a computer, and can bevolatile memory or nonvolatile memory. The memory has stored therein anumber of routines that are executable by the processor, includingroutines for implementing the disclosed concept as described herein. Inparticular, processing apparatus 206 includes a quantifying component208 configured for quantifying local spatial statistics for H&E stainedtissue images as described herein based on received image datarepresenting a H&E stained tissue image, an identifying component 210configured for identifying histological structures within the H&Estained tissue image based on the local spatial statistics as describedherein, and a segmented tissue image generating component 212 configuredfor generating a segmented H&E stained tissue image using the receivedimage data and the identified histological structures, which image maythen be provided to display 204. Quantifying component 208 may includeone or more components configured for quantifying local spatialstatistics by determining mutual information data indicative ofstatistical associations between neighboring pixels in the H&E imagedata, and identifying component 210 may include one or more componentsconfigured for identifying histological structures by using the mutualinformation data and a graph-based spectral segmentation algorithm asdescribed herein. Alternatively, quantifying component 208 may includeone or more components for identifying putative nuclei locations fromthe RGB data in the form of super pixels, building a superpixel graphbased on a pointwise distance between each superpixel and a number ofits nearest neighbors, and clustering the superpixels into labeledsegments, and identifying component 210 may include one or morecomponents configured for identifying by merging the labeled segmentsinto the histological structures as described herein.

FIG. 19 is a schematic diagram of an exemplary digital pathology system300 in which the methodology for quantifying spatial intratumorheterogeneity described herein may be implemented. As seen in FIG. 19,system 300 is a computing device structured to receive digital imagedata representative of fluorescence tissue images and process thoseimages as described herein. System 300 may be, for example and withoutlimitation, a PC, a laptop computer, a tablet computer, a smartphone, orany other suitable device structured to perform the functionalitydescribed herein. System 300 includes an input apparatus 302 (such as akeyboard), a display 304 (such as an LCD), and a processing apparatus306. A user is able to provide input into processing apparatus 106 usinginput apparatus 302, and processing apparatus 306 provides outputsignals to display 304 to enable display 304 to display information tothe user (such as spatial dependency images and PMI maps) as describedin detail herein. Processing apparatus 306 comprises a processor and amemory. The processor may be, for example and without limitation, amicroprocessor (μP), a microcontroller, or some other suitableprocessing device, that interfaces with the memory. The memory can beany one or more of a variety of types of internal and/or externalstorage media such as, without limitation, RAM, ROM, EPROM(s),EEPROM(s), FLASH, and the like that provide a storage register, i.e., amachine readable medium, for data storage such as in the fashion of aninternal storage area of a computer, and can be volatile memory ornonvolatile memory. The memory has stored therein a number of routinesthat are executable by the processor, including routines forimplementing the disclosed concept as described herein. In particular,processing apparatus 306 includes a cellular segmentation component 308configured for performing cellular segmentation on image datarepresenting a number of fluorescence tissue images to identify aplurality of cells of the number of fluorescence tissue images, anassigning component 310 configured for assigning each of the cells toone of a plurality of predetermined biomarker intensity patterns, aquantifying component 312 for quantifying spatial statistics for thenumber of fluorescence tissue images based on the assigned predeterminedbiomarker intensity patterns, and a visual representation generatingcomponent 314 for generating a visual representation of the quantifiedspatial statistics, such as a cell spatial dependency image 165 or a PMImap 170. Quantifying component 312 may include one or more componentsconfigured for quantifying the spatial statistics by constructing aspatial network to describe an organization of the predeterminedbiomarker intensity patterns in the number of fluorescence tissue imagesand quantifying the heterogeneity of the number of fluorescence tissueimages by computing pointwise mutual information for each pair of thepredetermined biomarker intensity patterns.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word “comprising” or “including”does not exclude the presence of elements or steps other than thoselisted in a claim. In a device claim enumerating several means, severalof these means may be embodied by one and the same item of hardware. Theword “a” or “an” preceding an element does not exclude the presence of aplurality of such elements. In any device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain elements are recited in mutuallydifferent dependent claims does not indicate that these elements cannotbe used in combination.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

What is claimed is:
 1. A method of identifying regions of interest in ahematoxylin and eosin (H&E) stained tissue image, comprising: receivingimage data representing the H&E stained tissue image; quantifying localspatial statistics for the H&E stained tissue image based on thereceived image data; identifying histological structures within the H&Estained tissue image based on the local spatial statistics; andgenerating a segmented H&E stained tissue image using the received imagedata and the identified histological structures.
 2. The method accordingto claim 1, wherein the image data is normalized image data created fromopponent color space data, and wherein the opponent color space data isgenerated by transforming original RGB data representing the H&E stainedtissue image into an opponent color space.
 3. The method according toclaim 1, wherein the image data is H&E image data in an opponent colorspace obtained by transforming RGB data representing the H&E stainedtissue image into the opponent color space.
 4. The method according toclaim 3, wherein the quantifying local spatial statistics comprisesdetermining mutual information data indicative of statisticalassociations between neighboring pixels in the H&E image data, andwherein the identifying histological structures uses the mutualinformation data and a graph-based spectral segmentation algorithm. 5.The method according to claim 4, wherein the H&E image data comprisesH&E-hue data in the opponent color space.
 6. The method according toclaim 5, wherein the opponent color space comprises a 3-channel spaceincluding an H&E-brightness channel, an H&E-saturation channel and anH&E-hue channel.
 7. The method according to claim 5, wherein thedetermining mutual information data comprises estimating a jointdistribution of hue angles between neighboring pixels in the H&E-huedata, and calculating a pointwise mutual information (PMI) of the jointdistribution, the PMI being the mutual information data.
 8. The methodaccording to claim 7, wherein the identifying comprises creating anaffinity function from the PMI and detecting boundaries based on theaffinity function using spectral clustering.
 9. The method according toclaim 7, wherein the estimating the joint distribution uses a mixture ofbivariate von Mises distribution.
 10. The method according to claim 1,wherein the image data is RGB data representing the H&E stained tissueimage, and wherein the quantifying local spatial statistics is based oninter-nuclei distance distributions determined from the RGB data. 11.The method according to claim 10, wherein the quantifying comprisesidentifying putative nuclei locations from the RGB data in the form ofsuperpixels, building a superpixel graph based on a pointwise distancebetween each superpixel and a number of its nearest neighbors, andclustering the super pixels into labeled segments, and wherein theidentifying comprises merging the labeled segments into the histologicalstructures.
 12. A non-transitory computer readable medium storing one ormore programs, including instructions, which when executed by acomputer, causes the computer to perform the method of claim
 1. 13. Acomputerized system for identifying regions of interest in a hematoxylinand eosin (H&E) stained tissue image, comprising: a processingapparatus, wherein the processing apparatus includes: a quantifyingcomponent configured for quantifying local spatial statistics for theH&E stained tissue image based on received image data representing theH&E stained tissue image; an identifying component configured foridentifying histological structures within the H&E stained tissue imagebased on the local spatial statistics; and a segmented tissue imagegenerating component configured for generating a segmented H&E stainedtissue image using the received image data and the identifiedhistological structures.
 14. The system according to claim 13, whereinthe image data is normalized image data created from opponent colorspace data, and wherein the opponent color space data is generated bytransforming original RGB data representing the H&E stained tissue imageinto an opponent color space.
 15. The system according to claim 13,wherein the image data is H&E image data in an opponent color spaceobtained by transforming RGB data representing the H&E stained tissueimage into the opponent color space.
 16. The system according to claim15, wherein the quantifying component is configured for quantifyinglocal spatial statistics by determining mutual information dataindicative of statistical associations between neighboring pixels in theH&E image data, and wherein the identifying component is configured foridentifying histological structures by using the mutual information dataand a graph-based spectral segmentation algorithm.
 17. The systemaccording to claim 16, wherein the H&E image data comprises H&E-hue datain the opponent color space.
 18. The system according to claim 17,wherein the opponent color space comprises a 3-channel space includingan H&E-brightness channel, an H&E-saturation channel and an H&E-huechannel.
 19. The system according to claim 17, wherein the determiningmutual information data comprises estimating a joint distribution of hueangles between neighboring pixels in the H&E-hue data, and calculating apointwise mutual information (PMI) of the joint distribution, the PMIbeing the mutual information data.
 20. The system according to claim 19,wherein the identifying comprises creating an affinity function from thePMI and detecting boundaries based on the affinity function usingspectral clustering.
 21. The system according to claim 19, wherein theestimating the joint distribution uses a mixture of bivariate von Misesdistribution.
 22. The system according to claim 13, wherein the imagedata is RGB data representing the H&E stained tissue image, and whereinthe quantifying component is configured for quantifying local spatialstatistics based on inter-nuclei distance distributions determined fromthe RGB data.
 23. The system according to claim 22, wherein thequantifying comprises identifying putative nuclei locations from the RGBdata in the form of superpixels, building a superpixel graph based on apointwise distance between each superpixel and a number of its nearestneighbors, and clustering the superpixels into labeled segments, andwherein the identifying component is configured for identifying bymerging the labeled segments into the histological structures.
 24. Amethod of quantifying intratumor cellular spatial heterogeneity influorescence tissue images, comprising: receiving image datarepresenting a number of fluorescence tissue images; performing cellularsegmentation on the received image data to identify a plurality of cellsof the number of fluorescence tissue images; assigning each of the cellsto one of a plurality of predetermined biomarker intensity patterns;quantifying spatial statistics for the number of fluorescence tissueimages based on the assigned predetermined biomarker intensity patterns;and generating a visual representation of the quantified spatialstatistics.
 25. The method according to claim 24, wherein thequantifying comprises constructing a spatial network to describe anorganization of the predetermined biomarker intensity patterns in thenumber of fluorescence tissue images and quantifying the heterogeneityof the number of fluorescence tissue images by computing pointwisemutual information for each pair of the predetermined biomarkerintensity patterns, wherein the visual representation is based on thecomputed point wise mutual information for each pair of thepredetermined biomarker intensity patterns.
 26. The method according toclaim 25, wherein the visual representation is a PMI map having aplurality of entries, and wherein the PMI map describes relationshipsbetween the predetermined biomarker intensity patterns.
 27. The methodaccording to claim 26, wherein each of the entries indicates howfrequently a particular spatial interaction between two of thepredetermined biomarker intensity patterns occurs in the image data whencompared to the interactions predicted by a random distribution over allpredetermined biomarker intensity patterns.
 28. The method according toclaim 27, wherein one or more of the entries is depicted in a firstcolor to denote a strong spatial association between predeterminedbiomarker intensity patterns and one or more of the entries is depictedin a second color to denote a week spatial association betweenpredetermined biomarker intensity patterns.
 29. The method according toclaim 28, wherein the entries are arranged in a plurality of rows and aplurality of columns.
 30. The method according to claim 24, wherein thevisual representation is an image showing spatial dependencies among thecells of the number of fluorescence tissue images using a plurality ofschematic representations, each schematic representation correspondingto one of the predetermined biomarker intensity patterns.
 31. Anon-transitory computer readable medium storing one or more programs,including instructions, which when executed by a computer, causes thecomputer to perform the method of claim
 24. 32. A computerized systemfor quantifying intratumor cellular spatial heterogeneity influorescence tissue images, comprising: a processing apparatus, whereinthe processing apparatus includes: a cellular segmentation componentconfigured for performing cellular segmentation on image datarepresenting a number of fluorescence tissue images to identify aplurality of cells of the number of fluorescence tissue images; anassigning component configured for assigning each of the cells to one ofa plurality of predetermined biomarker intensity patterns; a quantifyingcomponent for quantifying spatial statistics for the number offluorescence tissue images based on the assigned predetermined biomarkerintensity patterns; and a visual representation generating component forgenerating a visual representation of the quantified spatial statistics.33. The system according to claim 32, wherein the quantifying componentis configured for quantifying the spatial statistics by constructing aspatial network to describe an organization of the predeterminedbiomarker intensity patterns in the number of fluorescence tissue imagesand quantifying the heterogeneity of the number of fluorescence tissueimages by computing pointwise mutual information for each pair of thepredetermined biomarker intensity patterns, wherein the visualrepresentation is based on the computed point wise mutual informationfor each pair of the predetermined biomarker intensity patterns.
 34. Thesystem according to claim 33, wherein the visual representation is a PMImap having a plurality of entries, and wherein the PMI map describesrelationships between the predetermined biomarker intensity patterns.35. The system according to claim 34, wherein each of the entriesindicates how frequently a particular spatial interaction between two ofthe predetermined biomarker intensity patterns occurs in the image datawhen compared to the interactions predicted by a random distributionover all predetermined biomarker intensity patterns.
 36. The systemaccording to claim 35, wherein one or more of the entries is depicted ina first color to denote a strong spatial association betweenpredetermined biomarker intensity patterns and one or more of theentries is depicted in a second color to denote a week spatialassociation between predetermined biomarker intensity patterns.
 37. Thesystem according to claim 36, wherein the entries are arranged in aplurality of rows and a plurality of columns.
 38. The method accordingto claim 32, wherein the visual representation is an image showingspatial dependencies among the cells of the number of fluorescencetissue images using a plurality of schematic representations, eachschematic representation corresponding to one of the predeterminedbiomarker intensity patterns.